Semiconductor memory system including a plurality of semiconductor memory devices

ABSTRACT

A communication line is connected to first and second chips, and held at a first signal level. A monitor circuit changes a signal level of the communication line from the first signal to a second signal level while one of the first and second chips uses a current larger than a reference current. When the signal level of the communication line is the second signal level, the other of the first and second chips is controlled to a wait state that does not transfer to an operating state of using a current larger than the reference current.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 14/539,522 filedNov. 12, 2014. U.S. Ser. No. 14/539,522 is a divisional of U.S. Ser. No.14/073,521 filed Nov. 6, 2013 which is a divisional of U.S. Ser. No.13/598,099 filed Aug. 29, 2012, now U.S. Pat. No. 8,593,880, which is adivisional of U.S. Ser. No. 12/645,104 filed Dec. 22, 2009, now U.S.Pat. No. 8,284,607 which is a division of U.S. Ser. No. 12/027,546,filed Feb. 7, 2008, now U.S. Pat. No. 7,656,711, which is based upon andclaims the benefit of priority from prior Japanese Patent ApplicationNo. 2007-030789, filed Feb. 9, 2007, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a non-volatile semiconductor memorydevice, for example, a NAND flash memory. In particular, the presentinvention relates to a semiconductor memory system including a pluralityof built-in flash memories.

2. Description of the Related Art

A NAND flash memory requires the following threshold distribution withina limited threshold voltage range, for example, −2V to 5V. Specifically,if four values are given, four threshold distributions must be set. Ifeight values are given, eight threshold distributions must be set. If 16values are given, 16 threshold distributions are set. In a writesequence, a program operation and a verify operation are made, andprogram voltage is gradually stepped up to repeat the program operationand the verify operation. As described above, the program voltage isgradually stepped up to repeat the program operation and the verifyoperation; for this reason, write time increases. As a result, writeperformance must be enhanced, and simultaneously, the number of writecells increases.

When the program operation is started, all bit lines must be charged.Moreover, when a verify read operation is started, all bit lines arecharged to determine current carrying through all bit lines. Therefore,very large current is required, and thus, large peak current istemporarily generated.

The NAND flash memory is frequently used as the following multi-chippackage (MCP) and memory card. The multi-chip package (MCP) hassimultaneously some, for example, two to four built-in chips to increasestorage capacity. The memory card has a plurality of built-in chips. Asdescribed above, when some chips are built in, if the peak current ofeach chip overlaps, larger peak current is generated. For this reason,there is a possibility of causing a problem such as disconnectionreducing reliability.

In order to solve the foregoing problem, the following technique (e.g.,see Jpn. Pat. Appln. KOKAI Publication No. 11-242632) has beendeveloped. According to the technique, the peak value of currentgenerated is reduced when write is concurrently made with respect to aplurality of chips. However, it is desired to prevent an increase ofcircuit configuration and securely and sufficiently reduce the peakcurrent.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided asemiconductor memory system comprising: a first semiconductor memorydevice; a second semiconductor memory device; a common communicationline connected to the first and second semiconductor memory devices, andkept at a first level; and a control circuit connected to thecommunication line, a control signal changing a level of thecommunication line from the first level to the second level while one ofthe first and second semiconductor memory devices uses a current largerthan a reference current, and controlling the other of the first andsecond semiconductor memory devices to a wait state that does nottransfer to an operating state using a current larger than the referencecurrent when the level of the communication line is the second level.

According to a second aspect of the invention, there is provided asemiconductor memory system comprising: a first semiconductor memorydevice; a second semiconductor memory device; a control circuitconnected to the first and second semiconductor memory devices; and avoltage generation circuit provided in the control circuit, andgenerating a voltage, the control circuit supplying a voltage generatedby the voltage generation circuit to one of the first and secondsemiconductor memory devices.

According to a third aspect of the invention, there is provided asemiconductor memory system comprising: a first semiconductor memorydevice; a second semiconductor memory device; and a control circuitconnected to the first and second semiconductor memory devices, thecontrol circuit controlling program and verify operation of the firstand second semiconductor memory devices.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 shows a first embodiment, and is a view showing the configurationof a monitor circuit;

FIG. 2 is a view schematically showing the configuration of asemiconductor memory device according to a first embodiment;

FIG. 3 is a circuit diagram showing the configuration of a memory cellarray;

FIG. 4 is a circuit diagram showing another configuration of a memorycell array;

FIGS. 5A and 5B are cross-sectional views showing a memory cell and aselect transistor;

FIG. 6 is a cross-sectional view showing a NAND flash memory;

FIG. 7 is a table showing voltage supplied to each area shown in FIG. 4;

FIG. 8 is a circuit diagram showing the configuration of a data storagecircuit shown in FIGS. 3 and 4;

FIGS. 9A, 9B and 9C are views showing memory cell threshold voltagedistribution with write and erase operations;

FIG. 10 is a view showing a waveform when read, verify operation ismade;

FIG. 11 is a view showing a waveform when a program operation is made;

FIG. 12 is a flowchart to explain a first-page write operation;

FIG. 13 is a flowchart to explain a second-page write operation;

FIG. 14 is a circuit diagram showing the configuration of a sequencecontroller;

FIG. 15 is a circuit diagram showing the configuration of a timingsignal generation circuit;

FIG. 16 is a waveform chart showing an output signal of the timingsignal generation circuit;

FIG. 17 is a circuit diagram showing another configuration of a timingsignal generation circuit;

FIGS. 18A and 18B are circuit diagrams showing the configuration of apeak signal generation circuit;

FIG. 19 is a view to explain a program sequence;

FIG. 20 is a view showing the configuration of a second embodiment;

FIG. 21 is a view showing the configuration of a third embodiment;

FIG. 22 is a view showing the configuration of a fourth embodiment;

FIG. 23 is a view showing the configuration according to a modificationexample of the fourth embodiment;

FIG. 24 is a view showing the configuration according to a modificationexample of the first embodiment;

FIG. 25 is a view showing the configuration according to anothermodification example of the first embodiment;

FIG. 26 is a view showing the configuration according to a modificationexample of the fourth embodiment; and

FIG. 27 is a view showing the configuration according to a modificationexample of the fourth embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the present invention will be hereinafterdescribed with reference to the accompanying drawings.

The configuration and operation of one NAND flash memory will behereinafter described with reference to FIG. 2 to FIG. 13.

FIG. 2 is a view schematically showing the configuration of a NAND flashmemory storing the 2-bit four-value data, for example.

A memory cell array 1 includes a plurality of bit lines and word linesand a common source line. For example, an electrically rewritable memorycell comprising an EEPROM is arrayed like a matrix. The memory cellarray 1 is connected with a bit control circuit 2 for controlling a bitline and a word line control circuit 6.

The bit line control circuit 2 makes the following operations via thebit line. Specifically, the circuit 2 reads the data of a memory cell ofthe memory cell array 1. The circuit 2 detects a state of the memorycell of the memory cell array. The circuit further applies a writecontrol voltage to the memory cell of the memory cell array. The bitline control circuit 2 is further connected with a column decoder 3 anda data input/output buffer 4. A data storage circuit included in the bitline control circuit 2 is selected by the column decoder 3. Data of thememory cell read by the data storage circuit is output externally from adata input/output terminal 5 via the data input/output buffer 4.Externally supplied various commands CMD for controlling the operationof the NAND flash memory, address ADD and data DT are input to the datainput/output terminal 5. Write data input to the data input/outputterminal 5 is supplied to the data storage circuit selected by thecolumn decoder 3. The foregoing command and address are supplied to acontrol signal and control voltage generation circuit 7 via the buffer4.

The word line control circuit 6 is connected to the memory cell array 1.The word line control circuit 6 selects a word line included in thememory cell array 1. Then, the circuit 6 applies voltage required forread, write or erase to the selected word line.

The foregoing memory cell array 1, bit line control circuit 2, columndecoder 3, data input/output buffer and word line control circuit 6 areconnected to the control signal and control voltage generation circuit7, and controlled by the circuit 7. The control signal and controlvoltage generation circuit 7 is connected to a control signal inputterminal 8. The circuit 7 is controlled by the following controlsignals: address latch enable (ALE), command latch enable (CLE), writeenable (WE) and read enable (RE) externally input via the control signalinput terminal 8.

The foregoing bit line control circuit 2, column decoder 3, word linecontrol circuit 6 and control signal and control voltage generationcircuit 7 form a write circuit and a read circuit.

FIG. 3 shows each configuration of the memory cell array 1 and the bitline control circuit 2 shown in FIG. 2. The memory cell array 1 has aplurality of NAND cells arrayed. One NAND cell is composed of a memorycell MC, select gates S1 and S2. For example, the memory cell MCcomprises 32 EEPROMs connected in series. The select gate S2 isconnected to a bit line BL0 e while the select gate S1 is connected to asource line SRC. A control gate of the memory cell MC arrayed in eachrow is commonly connected to word lines WL0 to WL29, WL30 and WL31. Theselect gate S2 is commonly connected to a select line SGD while theselect gate S1 is commonly connected to a select line SGS.

The bit line control circuit 2 has a plurality of data storage circuits10. Each of the data storage circuits 10 is connected with a pair of bitlines (BL0 e, BL0 o), (BL1 e, BL1 o) . . . (BLie, BLio), (BL8 ke, BL8ko).

The memory cell array 1 includes a plurality of blocks shown by a brokenline. Each block comprises a plurality of NAND cells. For example, datais erased at a unit of the block. An erase operation is madesimultaneously with respect to two bit lines connected to the datastorage circuit 10.

A plurality of memory cells (in arrange surrounded by a broken line)form one sector. These memory cells are alternately arrayed andconnected to one word line. Data is written and read out every sector.In other words, half of the memory cells arrayed in the row directionare connected to the corresponding bit line. Thus, write or readoperation is carried out with respect to the foregoing half of thememory cells arrayed in the row direction.

In read, program verify and program operations, one of two bit lines(BLie, BLio) connected to the data storage circuit 10 is selected inaccordance with address signals (YA0, YA1, . . . YAi . . . YA8 k)supplied externally. In accordance with the external address, one wordline is selected, and thus, a second page shown by a broken line isselected. The changeover to the second page is made according to theaddress.

FIG. 4 shows another configuration of the foregoing memory cell array 1and bit line control circuit 2 shown in FIG. 2. According to theconfiguration shown FIG. 3, the data storage circuit 10 is connectedwith two bit lines (BLie, BLio). On the contrary, according to theconfiguration shown in FIG. 4, each bit line is connected with the datastorage circuit 10. The memory cells arrayed in the row direction areall connected to the corresponding bit line. Thus, a write or readoperation is carried out with respect to all memory cells arrayed in therow direction.

In the following description, both of the configurations shown in FIGS.3 and 4 are applicable. Here, the case of using the configuration shownin FIG. 3 will be hereinafter described.

FIGS. 5A and 5B are cross-sectional views showing a memory cell and aselect transistor. FIG. 5A shows a memory cell. A substrate 51 (P-wellregion 55 described later) is formed with an n diffusion layer 42functioning as source and drain of the memory cell. A floating gate (FG)44 is formed on the P-well region 55 via a gate insulating film 43. Acontrol gate (CG) 46 is formed on the floating gate 44 via a gateinsulating film 45. FIG. 5B shows a select gate. The P-well region 55 isformed with an n diffusion layer 47 functioning as source and drain. Acontrol gate 49 is formed on the P-well region 55 via a gate insulatingfilm 48.

FIG. 6 is a cross-sectional view showing a NAND flash memory. Forexample, a P-type semiconductor substrate 51 is formed with N-wellregions 52, 53, 54 and a P-well region. The P-well region is formed inthe N-well region 52. A memory cell Tr forming the memory cell array isformed in the P-well region 55. Low-voltage P-channel transistor LVPTrand low-voltage N-channel transistor LVNTr forming the data storagecircuit 10 are formed in the N-well region 53 and the P-well region 56,respectively. A high-voltage N-channel transistor HVNTr connecting thebit line and the data storage circuit 10 is formed in the substrate 51.A high-voltage P-channel transistor HVPTr forming a word line drivecircuit is formed in the N-well region 54. As seen from FIG. 5,high-voltage transistors HVNTr and HVPTr have a gate insulating filmthicker than low-voltage transistors LVNTr and LVPTr.

FIG. 7 is a table showing a voltage supplied to each region shown inFIG. 6. In erase, program, and read operations, a voltage shown in FIG.7 is supplied to each region. In FIG. 7, Vera is a voltage applied tothe substrate when data is erased. Vss is a ground voltage, and Vdd is apower supply voltage. Vpgmh is a voltage Vpgm+Vth supplied to the wordline when data is written. Vreadh is a voltage Vread+Vth supplied to theword line when data is read.

FIG. 8 is a circuit diagram showing the configuration of the datastorage circuit 10 shown in FIG. 3.

The data storage circuit 10 has a primary data cache (PDC), secondarydata cache (SDC), dynamic data cache (DDC) and temporary data cache(TDC). The foregoing SDC, PDC and DDC hold input data in a writeoperation, and hold in a read operation, and further, temporarily holddata in a verify operation. Moreover, these caches are used to handleinternal data when multi-value data is stored. The TDC amplifies data ofthe bit line when data is read, and temporarily holds it, and further,is used to handle internal data when multi-value data is stored.

The SDC is composed of clocked inverters 61 a, 61 b forming a latch,transistors 61 c and 61 d. The transistor 61 c is connected between aninput terminal of the clocked inverter 61 a and an input terminal of theclocked inverter 61 b. A gate of the transistor 61 c is supplied with asignal EQ2. The transistor 61 d is connected between an output terminalof the clocked inverter 61 and ground. A gate of the transistor 61 d issupplied with a signal PRST. A node N2 a of the SDC is connected to aninput/output data line IO via a column select transistor 61 e. A node N2b of the SDC is connected to an input/output data line Ion via a columntransistor 61 f. Each gate of these transistors 61 e and 61 f issupplied with a column select signal CSLi. The node N2 a of the SDC isconnected to a node N1 a of the PDC via transistors 61 g and 61 h. Agate of the transistor 61 g is supplied with a signal BLC2 while a gateof the transistor 61 h is supplied with a signal BLC1.

The PDC is composed of clocked inverters 61 i, 61 j and transistor 61 k.The transistor 61 k is connected between an input terminal of theclocked inverter 61 i and an input terminal of the clocked inverter 61j. A gate of the transistor 61 k is supplied with a signal EQ1. A nodeN1 b of the PDC is connected to a gate of a transistor 61 l. Oneterminal of a current path of the transistor 61 l is grounded via atransistor 61 m. A gate of the transistor 61 m is supplied with a signalCHK1. The other terminal of the current path of the transistor 61 l isconnected to one terminal of a current path of transistors 61 n and 61 oforming a transfer gate. A gate of the transistor 61 n is supplied witha signal CHK2 n. A gate of the transistor 61 o is connected to an outputterminal of the clocked inverter 61 a. The other terminal of the currentpath of the transistors 61 n and 61 o is connected with an interconnectCOMi. The interconnect COMi is an interconnect common to all datastorage circuits 10. When verify of all data storage circuit 10 iscompleted, the potential of the interconnect COMi goes high. Namely,when verify is completed, a node N1 b of the PDC goes low, as describedlater. In this state, when the signals CHK1 and CHK2 are made high, ifverify is completed, the potential of the interconnect COMi goes high.

The TDC comprises a MOS capacitor 61 p, for example. The capacitor 61 pis connected between a connection node N3 of the transistors 61 g, 61 hand ground. The connection node N3 is further connected with the DDC viaa transistor 61 q. A gate of the transistor 61 q is supplied with asignal REG.

The DDC is composed of transistors 61 r and 61 s. One terminal of acurrent path of the transistor 61 r is supplied with a signal VREG whilethe other terminal thereof is connected to a current path of thetransistor 61 q. A gate of the transistor 61 r is connected to the nodeN1 a of the PDC via the transistor 61 s. A gate of the transistor 61 sis supplied with a signal DTG.

The connection node N3 is further connected with one terminal of acurrent path of transistors 61 t and 61 u. The other terminal of thecurrent path of the transistor 61 u is supplied with a signal BLCLAMP.The other terminal of the current path of the transistor 61 t isconnected to one terminal of the bit line BLo via a transistor 61 v, andconnected to one terminal of the bit line BLe via a transistor 61 w. Theother terminal of the bit line BLo is connected to one terminal of acurrent path of a transistor 61 x. A gate of the transistor 61 x issupplied with a signal BIASo. The other terminal of the bit line BLe isconnected to one terminal of a current path of a transistor 61 y. A gateof the transistor 61 y is supplied with a signal BIASe. The otherterminal of a current path of these transistors 61 x and 61 y issupplied with a signal BLCRL. Transistors 61 x and 61 y are turned oncomplementarily to transistors 61 v and 61 w in accordance with signalsBIASo and BIASe to supply a potential of the signal BLCRL to anon-select bit line.

The foregoing signals and voltages are generated by the control signaland control voltage generation circuit 7 shown in FIG. 3. The followingoperation is controlled based on the control by the control signal andcontrol voltage generation circuit 7.

The data storage circuit 10 shown in FIG. 4 has the same configurationas shown in FIG. 8. In this case, connection with the bit line isdifferent only. Specifically, the other terminal of the transistor 61 tis connected with the transistor 61 v only, and connected to bit linesBLe or BLo via the transistor 61 v.

The present memory is a multi-value memory, and stores two-bit data inone cell. Changeover to two-bit is made according to address (firstpage, second page). If two bits are stored in one cell, two pages arerequired. If three bits are stored in one cell, changeover is madeaccording to address (first page, second page, third page). If four bitsare stored in one cell, changeover is made according to address (firstpage, second page, third page, fourth page).

FIGS. 9A, 9B and 9C show the relationship between data and thresholdvoltage when two-bit data is stored in a memory cell. When an eraseoperation is made, the data of the memory cell becomes “0” as seen fromFIG. 9C. After erase is made, write is made using a verify level “z” tonarrow down a spread of the threshold distribution. The data “0” is setas negative threshold voltage distribution.

As shown in FIG. 9A, if write data is “1” in first page write, memorycell data is still “0”. If the write data is “0”, the memory cell databecomes “1”.

As depicted in FIG. 9B, the second page is written, and thereafter,memory cell data is given as any of “0”, “2”, “3” and “4” in accordancewith write data. Specifically, when memory cell data is “0” after thefirst page is written and the write data of the second page is “1”, thememory cell data is still “0”. When the write data is “0”, memory celldata is “2”. Moreover, when memory cell data is “1” after the first pageis written and the write data is “0”, memory cell data is “3”. Whenwrite data is “1”, memory cell data is “4”. According to thisembodiment, the memory cell data is defined as being changed from lowthreshold voltage to high threshold voltage. In this case, data “1”,“2”, “3” and “4” are a positive threshold voltage.

(Read Operation)

As seen from FIG. 9, the first page is written, and thereafter, memorycell data exists as data “0” or “1”; therefore, a read operation is madeat a level “a”. The second page is written, and thereafter, memory celldata exists as any of “0”, “2”, “3” and “4”. Therefore, a read operationis made at any of levels “b”, “c” and “d”.

FIG. 10 shows each waveform of read and read verify operations. In theread operation, well, source line and non-select bit line of theselected cell are set as 0V.

A potential “a” (e.g., “a”=0V), “b”, “c2 or “d” in the read operation isapplied to a select word line. Simultaneously, a non-select word line ofa select block is set as Vread, and a select line SGD of the selectblock is set as Vsg (=Vdd+Vth). In this way, the select line SGS is setto Vss. Voltages Vdd (e.g., 2.5V), Vsg and (0.6V+Vth) are temporarilyapplied to VPRE, BLPRE and BLCLAMP of the data storage circuit shown inFIG. 8, respectively. In this way, the bit line is pre-charged to 0.6V,for example.

In this case, the select bit line is 0.6V, and the non-select bit lineis Vss. Thus, if the capacitance of one bit line, non-select bit line,well and source is set as 4 pF, the capacitance Q of one bit line isobtained from the following equation Q=C×V, that is, Q=4 pF×0.6V. Forexample, if 8 kB is simultaneously written, the capacitance Q isobtained from the following equation Q=8×1024×8×4 pF×0.6V. For thisreason, large peak current is generated as shown in FIG. 10.

The select line SGS on the source side of the cell is set as Vsg(=Vdd+Vth). When the threshold voltage is higher than “a” or “b”, “c”and “d”, the cell turns off. Thus, the bit line is still high (e.g.,0.6V). When the threshold voltage is lower than “a” or “b”, “c” and “d”,the cell turns on. Thus, the bit line is discharged to become the samepotential as the source, that is, Vss.

The signal BLPRE of the data storage circuit shown in FIG. 8 istemporarily set to Vsg (=Vdd+Vth) to pre-charge the node of the TDC toVdd. Thereafter, the signal BLCLAMP is supplied with a voltage(0.45+Vth), for example. When the bit line is lower than 0.45V, the nodeof the TDC goes low. Conversely, when the bit line is higher than 0.45V,the node of the TDC is still high. In FIG. 10, the signal BLC1 is set toVsg (=Vdd+Vth) so that the PDC reads the potential of the TDC.Therefore, if the threshold voltage of the cell is lower than level “a”or “b”, “c” and “d”, the PDC goes low. Conversely, the threshold voltageis higher than above, the PDC goes high, and thus, read is made.

As shown in FIG. 4, when all cells array in the row direction arecollectively read, the select line SGS of the select block is made hightogether with the select line SGD of the select block. Thus, when thebit line is charged, and simultaneously, the cell is on, the bit line isdischarged. Conversely, when the cell is off, the bit line is held at acharging state. The bit line level is read to the PDC via the TDC.Therefore, if the number of on-state cells is much, large current flowsthrough the source line from the node supplied with the signal VPRE. Asa result, there is a problem that the potential of the source line is afloating state. In order to solve the problem, a read operation is madeseveral times. When the cell turns on, that is, the cell through whichcurrent flows determines the read result as low level not to charge thebit line from the next time. In the first-time read, read is again madewith respect to the cell, which is read at high level. Therefore, largepeak current is generated in the first-time read.

(Program and Program Verify)

(Program)

FIG. 11 shows a waveform of a program operation. FIG. 12 is a flowchartshowing a first page program operation. FIG. 13 is a flowchart showing asecond page program operation. The program operation will beschematically described with reference to FIGS. 12 and 13.

According to the program operation, address is designated, and then, twopages shown in FIG. 3 are selected. In this memory, of two pages,program is made in the order of first page and second page. Therefore,the first page is selected at first.

Write data is externally input, and then, stored in the SDC of all datastorage circuits 10 (step S11). When a write command is input, data ofthe SDC of all data storage circuits 10 is transferred to the PDC (stepS12). When data “1” (no write is made) is externally input, the node N1a of the PDC goes high. Conversely, when data “0” (write is made) isinput, the node N1 a goes low. Thereafter, the data of the PDC is set asthe potential of the node N1 a of the data storage circuit 10. On theother hand, the data of the SDC is set as the potential of the node N2 aof the data storage circuit 10.

(Program Operation)

The signal BLC1 of the data storage circuit shown in FIG. 8 is set to avoltage Vdd+Vth. Thus, when the PDC stores data “1” (no write is made),the bit line is Vdd. Conversely, when the PDC stores data “0” (write ismade), the bit line is Vss. Write must not be made with respect to cells(bit line is non-select) of the non-select page connected to theselected word line. Thus, hit lines connected to these cells are set toVdd.

In this case, when write is made with respect to the select bit line(Vss), the non-select bit line is non-write (Vdd). The capacitance ofone select bit line, non-select bit line well and source is set as 4 pF,for example. A charge Q of one bit line is obtained from the followingequation Q=C (4 pF)×V (2.5V). For example, if 8 kB memory cells aresimultaneously written, the charge Q is obtained from the followingequation Q (8 kB)=8×1024×8×c (4 pF)×V (2.5V). Therefore, large peakcurrent is generated.

As depicted in FIG. 4, when all memory cells arrayed in the rowdirection are collectively written, all bit lines are a selected state.In particular, when data “1” and data “0” are alternately given as writedata for example, the capacitance between all bit lines becomes themaximum. Therefore, large peak current is generated.

Vdd is applied to the select line SGD of the selected block, and a writevoltage VPGM (20V) is applied to the select word line, and further,VPASS (10V) is applied to the non-select line. The foregoing voltage isapplied, and thereby, when the bit line is Vss, a channel of the cell isVss, and the word line is VPGM; therefore, write is carried out. On theother hand, when the bit line is Vdd, the channel of the cell is Vdd,and not Vss. Thus, voltage is about VPGM/2 according to coupling; forthis reason, the memory cell is not programmed.

In the first page write (FIG. 12, S11 to S15), memory cell data becomesdata “0” and data “1”. After the second page write (FIG. 13, S21 toS28), memory cell data becomes data “0”, “2”, “3” and “4”.

(Program Verify Read)

The memory cell is written in the order of the level that thresholdvoltage is low. Thus, first page program verify is verified at a level“a′”, and second page program verify is verified at a level “b′”, “c′”or “d′” (S25 to S27). The program verify operation is almost the same asthe foregoing read operation.

Well, source line and non-select bit line of the selected cell is set toVss. A potential “a′”, “b′”, “c′” or “d′” (e.g., “a”=0V, “a′”=0.5V)slightly higher than the potential “a” in the read operation is appliedto the select word line. Hereinafter, the symbol “′” shows a verifyvoltage, and has a value slight higher than the read potential.

The signal VPRE of the data storage circuit 10 shown in FIG. 8 is set toVdd (e.g., 2.5V). The signal BLPRE is set to Vsg (=Vdd+Vth). The signalBLCLAMP is set to (0.6V+Vth). In this way, the bit line is pre-chargedto 0.6V. The select line SGS on the source side of the cell is set toVsg (=Vdd+Vth). Well and source line are Vss. Thus, when the thresholdvoltage is higher than “a′”, “b′”, “c′” or “d′”, the cell turns off.Thus, the bit line still high (e.g., 2.2V). Conversely, when thethreshold voltage is lower than “a′”, “b′”, “c′” or “d′”, the cell turnson. Thus, the bit line is discharged, and then, set as Vss. While thebit line discharges, the signal VPRE is set to Vss, and the signal BLPREis set to Vdd. Then, the TDC is set to Vss, the signal REG is made high,and further, the signal VREG is made high. In this way, the data of theDDC is moved to the TDC. Thereafter, the signal DTG is temporarily setto Vsg (=Vdd+Vth), the data of the PDC is copied to the DDC. The signalBLC1 is made high so that the data of the TDC is moved to the PDC. Viathe foregoing operation, data showing write or non-write stored in thePDC is transferred to the DDC, and then, the data of the DDC istransferred to the PDC.

The signal BLPRE is temporarily set to Vsg (=Vdd+Vth) to pre-charge thenode N3 of the TDC to Vdd. Thereafter, the signal BLCLAMP is set to(0.45V+Vth), for example. The node N3 of the TDC goes low when the bitline is lower than 0.45V. Conversely, when the bit line is higher than0.45V, the node N3 is still high. The signal BLC1 is set to Vsg(=Vdd+Vth) to read the potential of the TDC. Then, the signal VREG isset to Vdd, and the signal REG is set to Vsg (=Vdd+Vth). In this way,when the DDC is high (non-write), the TDC is forcibly made high.However, when the DDC is low (write), the value of the TDC has nochange. Here, the signal DTG is set to Vsg (=Vdd+Vth) so that the dataof the PDC is transferred to the DDC. Thereafter, the signal BLC1 is setto Vsg (=Vdd+Vth) to read the potential of the TDC to the PDC.Therefore, when the PDC is inherently low (write) and the thresholdvoltage of the cell is lower than level “a′”, “b′”, “c′” or “d′”, thePDC again goes low (write). Conversely, when the threshold voltage ofthe cell is higher than level “a′”, “b′”, “c′” or “d′”, the PDC goeshigh, and is set as non-write from the next program. When the PDC isinherently high (non-write), the PDC goes high, and is set as non-writefrom the next program.

In the second page write, according to the level “b′” program verify,when the foregoing operation is made, write cell to level “c′” and “d′”is set as non-write by the level “b′” program verify. For example, inthe case of level “c′” and “d′” write, the node N2 a of the data storagecircuit shown in FIG. 8 is made low. In the case of level “b′” write,the node N2 a is made high. In this state, the signal REG is set to Vsg.In the case of non-write, the signal BLC2 is set to Vtr (=0.1V+Vth)before an operation of forcibly making the TDC high. In the case oflevel “c′” and “d′” write, the TDC is forcibly made low so that write isnot completed in the level “b′” program verify.

Moreover, in the second page write, according to the level “c′” programverify, when the foregoing operation is made, write cell to level “d′”is set as non-write by the level “c′” program verify. For example, inthe case of level “c′” write, the data of the DDC of the data storagecircuit shown in FIG. 8 is previously made low. While the bit linedischarges, an exchange between the data of the PDC and the data of theDDC is made. Thus, the signal BLC1 is set to Vtr (=0.1V+Vth) before anoperation of forcibly making the TDC high. In the case of level “d′”write, the TDC is forcibly made low so that write is not completed inthe level “d′” program verify.

When the PDC is low, a write operation is again made, and the programoperation and the verify operation are repeated until the data of PDCsof all data storage circuits 10 become high.

As shown in FIG. 4, all memory cells arrayed in the row direction arecollectively program-verified. In this case, data is read and verifiedfrom all memory cells like the case of collectively reading all memorycells arrayed in the row direction.

(Erase Operation)

An erase operation is made at a unit of the block shown by the brokenline in FIGS. 3 and 4. After erase, the cell threshold voltage is thesame memory cell data “0” as seen from FIG. 9C.

First Embodiment

FIG. 1 is a view schematically showing the configuration of an MCP ormemory card using a NAND flash memory according to a first embodiment.In FIG. 1, for simplification of explanation, two NAND flash memorychips are built therein. In this case, chips more than two may be builtin.

In FIG. 1, the MCP has first, second chips 71, 72 and controller 73. Thefirst and second chips 71 and 72 include the NAND flash memory havingthe foregoing configuration. The controller 73 supplies chip enablesignal CE (A), CE (B) to the first and second chips 71 and 72. Thecontroller 73 further supplies a signal R/B showing Ready/busy, theforegoing signals ALE, CLE, WE, RE, address signal and data. Thecontroller 73 receives the data read from the first and second chips 71and 72, and outputs externally.

The foregoing first, second chips 71, 72 and controller 73 each have amonitor circuit MNT. The monitor circuit MNT monitors whether or not thefirst, second chips 71, 72 and controller 73 use current (peak current)larger than a reference current.

Each of the monitor circuits of the foregoing first, second chips 71, 72and controller 73 has the same configuration. For example, the monitorcircuit MNT of the first chip 71 is composed of an N-channel MOStransistors 74-1 and an inverter 75-1. Likewise, the monitor circuit MNTof the second chip 72 is composed of an N-channel MOS transistor 74-2and inverter 75-2. The monitor circuit MNT of the controller 73 iscomposed of an N-channel MOS transistor 74-3 and an inverter 75-3. Eachdrain of transistors 74-1, 74-2 and 74-3 is connected to a resistor 76included in the controller 73 via a communication line ML, and further,connected to power supply VDD via the resistor. Each source oftransistors 74-1, 74-2 and 74-3 is grounded. Each gate of transistors74-1, 74-2 and 74-3 is supplied with a peak signal PEAK generated ineach if the first, second chips 71, 72 and controller 73. Each inputterminal of the inverters 75-1, 75-2 and 75-3 is connected to each drainof the transistors 74-1, 74-2 and 74-3. Each output terminal of theinverters 75-1, 75-2 and 75-3 is connected to each internal circuit ofthe first, second chips 71, 72 and controller 73 described later.

Incidentally, a diode-connected N-channel depletion-type MOS transistor77 may be used in place of the resistor 76.

Any or both of the first and second chips are provided with the resistor76 without connecting to each drain of the transistors 74-1 and 74-2 tothe controller 73. In this way, power is supplied to transistors 74-1and 74-2 every first and second chips, and power is supplied to thesecond or first chip from the first or second chip.

As illustrated in FIG. 24, the following configuration may be employed.For example, a peak signal PEAK generated in the first chip 71 isinverted by an inverter 71-1 to be directly supplied to an inputterminal of an inverter 72-1 generating a monitor signal MOUT of thesecond chip 72. A peak signal PEAK generated in the second chip 72 isinverted by an inverter 72-2 to be directly supplied to an inputterminal of an inverter 71-2 generating a monitor signal MOUT of thefirst chip 71. In this case, a first peak recognition signal is suppliedfrom the first chip 71 to the second chip 72 while a second peakrecognition signal is supplied from the second chip 72 to the first chip71. Thus, two communication lines are required to make a connectionbetween the first and second chips 71 and 72.

The peak signal PEAK is a signal generated at peak current generationtiming in the first, second chips 71, 72 and controller 73, as describedlater. In other words, the peak signal PEAK is generated at timing whenlarge current such as write (program), verify read, read and erase isgenerated in the first and second chips 71 and 72.

The controller 73 further has an error correction circuit 78. When theerror correction circuit 78 is operated, large current is generated.Thus, when the read data is output, the peak signal PEAK is generated attiming when the error correction circuit 78 is operated.

If no peak current is generated, the peak signal PEAK is non-active(low). The potential (peak recognition signal) of each drain of thetransistors 74-1, 74-2 and 74-3 is made high. The monitor signal MOUToutput from each output terminal of the inverters 75-1, 75-2 and 75-3 ismade high. In this state, the first chip 71 attains a program state, andthen, when the peak signal PEAK is generated, the transistor 74-1 turnson; as a result, the communication line ML goes low. Thus, each monitorsignal MOUT output from the output terminals of the inverters 75-1, 75-2and 75-3 of the first, second chips 71, 72 and controller 73 goes high.When the monitor signal MOUT goes high, the second chip 72 and thecontroller 73 are in a wait state. Therefore, the second chip 72 and thecontroller 73 serves to prevent large current from being generated.

FIG. 14 shows the configuration of a sequence controller of the firstand second chips 71 and 72. The sequence controller is provided in thecontrol signal and control voltage generation circuit 7 shown in FIG. 2.

As seen from FIG. 14, the sequence controller is composed of a pluralityof flip-flops 81-1 to 81-n, AND gates 82-1 to 82-9, OR gates 82-10 and82-11. Each of flip-flops 81-1 to 81-n sequentially holds each stepstate of write operations shown in FIGS. 11 and 12. Specifically, theflip-flop 81-1 is set when data is transferred from the SDC to the PDCin accordance with a program command PGMCOM. The flip-flop 81-2 is setto a program start state after data is transferred from the SDC to thePDC. The flip-flop 81-3 is set to a program wait state. The flip-flop81-n is set to a verify start state after the program ends.

An input terminal of the AND gate 82-1 is supplied with a signal outputfrom the flip-flop 81-1 and a signal STPEND indicative that data istransferred from the SDC to the PDC. The flip-flop 81-1 is set accordingto the program command PGMCOM to output a signal STP, and then, resetaccording to an output signal of the AND gate 82-1.

Input terminals of AND gates 82-2 to 82-9 are supplied with the monitorsignal MOUT output from the corresponding inverter of the inverters 75-1and 75-2 forming the monitor circuit MNT included in the first andsecond chips 71 and 72.

Each input terminal of AND gate 82-2 and 82-6 is supplied with signalsSTP and STPEND. AND gates 82-3 and 82-7 receive a set output signal WPGMof the flip-flop 81-3. AND gates 81-4 and 82-8 are supplied with asignal VFY showing a verify state supplied from the flip-flop 81-n and asignal VFYEND indicative that verify ends supplied from a flip-flop (notshown).

The OR gate 82-10 receives output signals from AND gates 82-2, 82-3 and82-4 to set the flip-flop 81-2. As a result, the flip-flop 81-2 outputsa signal PGM showing a program state. The AND gate 82-5 receives asignal PGM output from the flip-flop 81-2 and a signal PGMEND indicativethat program ends. Then, the AND gate 82-5 resets the flip-flop 81-2 atinput timing of the signal PGMEND.

The OR gate 82-11 receives output signals from AND gates 82-6, 82-7 and82-8 to set the flip-flop 81-3. As a result, the flip-flop 81-3 outputsa signal WPGM showing a program wait state.

The AND gate 82-9 receives a signal PGM output from the flip-flop 81-2and a signal PGMEND indicative that program ends. The flip-flop 81-n isset according to an output signal from the AND gate 82-9, and outputs asignal VFY showing a verify operation state.

FIG. 15 shows the configuration of a timing signal generation circuit.FIG. 16 shows output signals of the timing signal generation circuit.

In FIG. 15, a clock generator 83 generates a clock signal CLK. A counterclock signal output from the clock generator 83 is supplied to a counter84. The counter 84 outputs counter timing signals TM0, TM1 . . . TMnshown in FIG. 16 according to the clock signal CLK. A rise recognitioncircuit 85 is supplied with output signals STP, PGM, WPGM, and VFY . . .from flip-flops 81-1 to 81-n. The rise recognition circuit 85 recognizesthe rise of each signal, and outputs a reset signal. For example, therise recognition circuit 85 outputs a reset signal just after PGM(program), VFY (verify) sequence comes in, and in this way, resets thecounter 84.

FIG. 17 shows the configuration of a timing signal generation circuitapplied to the program operation shown in FIG. 11. The timing signalgeneration circuit is composed of a plurality of AND gates 86-0, 86-1 .. . and a plurality of flip-flops 87-0, 87-1 . . . . An input terminalof the AND gate 80-1 is supplied with the following signals. One is asignal PGM showing a counter program state supplied from the flip-flop81-2 shown in FIG. 14. Another is inverted timing signals TM0, TM1 andTM2 supplied from the counter 84 shown in FIG. 15. An output signal ofthe AND gate 86-0 is supplied to a set input terminal of the flip-flop87-0. The flip-flop 87-0 is set when the input conditions of timingsignals TM0, TM1 and TM2 are satisfied in a program state, and thus,outputs a timing signal PCLK0. An input terminal of the AND gate 86-1 issupplied with the following signals. One is a signal PGM showing aprogram state, and another is timing signals TM0 and TM1 and invertedtiming signal TM2. An output signal of the AND gate 86-1 is supplied toa set input terminal of the flip-flop 87-1. The flip-flop 87-1 is setwhen the input conditions of timing signals TM0, TM1 and TM2 aresatisfied in a program state, and thus, outputs a timing signal PCLK1,while resets the timing signal PCLK0.

In FIG. 17, there are only shown circuits generating timing signalsPLCK0 and PLCK1. In this case, circuits generating timing signals PLCK2to PLCK4 (PGMEND) have the same configuration as above. Further,circuits generating timing signals PLCK0 to PLCK4 (READEND, VRYEND)applied to read and verify read operations shown in FIG. 10 have thesame configuration as above.

FIG. 18A shows the configuration of a circuit, which included in each ofthe first and second chips 71 and 72 shown in FIG. 1, and generates apeak signal PEAK in program, read or verify read operation. For example,the circuit is composed of OR gates 88-1, 88-2 and a flip-flop 88-3. Aninput terminal of the OR gate 88-1 is supplied with timing signals PCLK0and RCLK0. An input terminal of the OR gate 88-2 is supplied with timingsignals PCLK1 and RCLK1. These timing signals RCLK0 and RCLK1 are timingsignals generated like the foregoing program in read and verify readoperation. An output terminal of the OR gate 88-1 is connected to a setinput terminal of the flip-flop 88-3. An output terminal of the OR gate88-2 is connected to a reset input terminal of the flip-flop 88-3. Apeak signal PEAK is output from an output terminal of the flip-flop88-3. Specifically, as seen from FIGS. 10 and 11, the peak current isgenerated between timing signals RCLK0 and RCLK1 or between PCLK0 andPCLK1 in read, verify read or program operation. In other words, thecircuit generating the peak signal PEAK generates a peak signal PEAKbetween timing signals RCLK0 and RCLK1 or between PCLK0 and PCLK1 inread, verify read or program operation.

FIG. 18B shows the configuration of a peak signal generation circuitincluded in the foregoing controller 73. The circuit comprises aflip-flop 88-4. A set input terminal of the flip-flop 88-4 is suppliedwith a timing signal ECCCLK0 while a reset input terminal thereof issupplied with a timing signal ECCCLK1. These timing signals ECCCLK0 andECCCLK1 show an operating period of the error correction circuit 78 ofthe controller 73. When the error correction circuit 78 is operated, apeak current is generated. The flip-flop 88-4 generates a peak signalPEAK between timing signals ECCCLK0 and ECCCKL1.

The peak signal PEAK generated in the circuit shown in FIG. 18A issupplied to the gate of transistors 74-1 or 74-2 forming the monitorcircuit MNT of the first and second chips shown in FIG. 1. The peaksignal PEAK generated in the circuit shown in FIG. 18B is supplied tothe gate of the transistor 74-3 forming the controller 73 shown in FIG.1.

When the peak signal PEAK is activated (made high) by the monitorcircuit of any of the first, second chips 71, 72 and controller 73, anyof transistors 74-1, 74-2 and 74-3 of the first, second chips 71, 72 andcontroller 73 turns on. In this way, the monitor signal MOUT output fromthe inverters 75-1, 75-2 and 75-3 is activated (made high). As a result,the input condition of the AND gates 82-1 to 82-4 is not satisfied, chipor controller except chip or controller activating the peak signal PEAKis in a wait state when it moves to program or read sequence generatingpeak current. Thereafter, program, read, verify read or error correctionend, and the input condition of any of AND gates 88-1, 88-2 and 88-4 isnot satisfied. Thus, the peak signal PEAK is not activated (made low).Therefore, when other chip or controller is a wait state, it can move toprogram or read sequence generating the next current peak.

For example, if three chips are connected, the first chip attains acurrent peak mode, and second and third chips are in a wait state. Inthis state, when the current peak mode period of the first chip ends,the second and third chips simultaneously come into a current peak mode.Therefore, in the case of MCP or memory card including three chips ormore, for example, priority is set in the order of the first, second andthird chips. The priority is set in the following manner. Specifically,the time until the chip actually comes into a current peak mode fromenabling to current peak mode is previously determined. For example, thefirst chip is set as 0 ns, the second chip is set to 100 ns, and thethird chip is set as 200 ns. The foregoing setting is made, and thereby,the second chip comes into the current peak mode after 100 ns, and thethird chip attains a wait state. When the second chip is released fromthe current peak mode, if the first chip does not come into the currentpeak mode, the third chip comes into the current peak mode after 200 ns.In this way, in the MCP or memory card including three chips, it ispossible to prevent peak current from being overlapped.

FIG. 25 shows another modification example of the MCP or memory cardhaving three chips. As shown in FIG. 25, according to the modificationexample, a first chip 71 outputs a first wait signal to second and thirdchips 72 and 100 in addition to a peak recognition signal. The secondchip 72 outputs a second wait signal to the third chip 100. When thefirst wait signal supplied from the first chip 71 is enable, the secondchip 72 does not come into a current peak mode. When the first or secondwait signal is enable, the third chip 100 does not come into a currentpeak mode. The foregoing configuration is employed, and thereby,priority is given to the third chip.

FIG. 19 shows the case where the second chip 72 makes a write operationin a slightly delayed state after the first chip 72 starts a writeoperation. The first and second chips 71 and 72 operate according to thewrite sequence of FIG. 11 to FIG. 13. When the operation starts, neitherthe first nor second chips 71 and 72 generate peak current. Thus, thepeak recognition signal (each drain voltage of transistors 74-1, 74-2and 74-3) goes high. Thereafter, when the first chip comes into aprogram state, peak current is generated. According to the foregoingoperation, the peak recognition signal goes low. In this state, even ifthe second chip 72 transfers to a program state, the peak recognitionsignal is low, and the monitor signal MOUT is high. Thus, the secondchip 72 is set to a wait state. Thereafter, the current of the firstchip 71 is released from a peak state, and then, the peak recognitionsignal goes high according to the foregoing operation. Therefore, themonitor signal MOUT goes low, and thus, the second chip 72 istransferred from the wait state to a program state.

According to the first embodiment, the first, second chips 71, 72 andcontroller 73 are each provided with the monitor circuit MNT monitoringthe peak current, and connected with each monitor circuit MNT. If peakcurrent is generated in any of the first, second chips 71, 72 andcontroller 73, other circuits are set to a wait state. Therefore, it ispossible to the peak current from being overlapped, and this serves toreduce large current consumption.

Each of the first, second chips 71, 72 and controller 73 has the monitorcircuit MNT, and generates a peak signal PEAK during the period whenpeak current generates. In this way, other monitor circuit MNT connectedvia the communication line ML is set to the same state. Therefore, aplurality of chips and the controller are set to a wait state andreleased from the wait state using the foregoing simple configuration.As a result, an increase of the chip area can be prevented.

According to the first embodiment, when peak current is generated, thepeak recognition signal is made low so that other chip does not transferto a sequence of generating peak current. In this case, if communicationtime is taken between some chips, the peak recognition signal is madelow slightly before peak current is generated. In this way, thegeneration of peak current may be indicated.

Voltage for charging the bit line is different between program, read andverify read. The peak current is larger in the program operation. Thus,when the peak current of the read and verify read operations has notproblem, the peak current is monitored in the program operation only.

According to the first embodiment, the NAND flash memory includes twochips; in this case, it may include one or three chips or more.

For example, if three chips are used, a plurality of peak recognitionsignals is prepared. When the first chip is in a program state andgenerates peak current, other two chips are set not to come into aprogram state. On the other hand, when the first chip is in a read stateand generates peak current, other two chips are not transferred to aprogram state. In this case, one chip only may be come into a readstate.

Likewise, a plurality of peak recognition signals is used in accordancewith the magnitude of peak current between plural NAND flash memoriesand the controller. In this way, it is possible to control so that thepeak current of the MCP or card does not become large.

In FIG. 1, some memories and the controller are shown. In this case, ifthe current of the controller does not become the peak, communication ismade between some memories only so that the peak is not overlapped.

Second Embodiment

As described above, each chip has an internal clock generation circuitfor controlling program and read sequences. The cycle (period) of aclock signal generated from the clock generation circuit is set bytrimming a resistance value in a die sort test. The cycle of the clocksignal generated from the clock generation circuit of each chip isslightly different. Thus, as illustrated in FIG. 19, when the first andsecond chips repeat program and verify read operations, even if overlapof peak current is first prevented, the peak current is graduallyoverlapped. For this reason, a wait state is frequently generated; as aresult, write performance is reduced. In order to solve the foregoingdisadvantage, the second embodiment relates to technique of controllinga plurality of chips and the controller using one clock signal.

FIG. 20 shows an MCP or card according to the second embodiment. In FIG.20, the same reference numbers are used to designate the same portionsas the first embodiment. According to the second embodiment, one offirst, second chips 71, 72 comprising a NAND flash memory or controller73 outputs a clock signal CLK. For example, if the controller 73 outputsthe clock signals, the first and second chips 71 and 72 effects program,read and verify read operations based on the clock signal supplied fromthe controller 73.

According to the second embodiment, the first, second chips 71, 72 andthe controller 73 are operated based on one clock signal. Thus, ascompared with the case where a plurality of clock signals is used, it ispossible to prevent the generation timing of peak current from beingoverlapped due to the shift between clock signals. Therefore, a waitoperation is not frequently generated, and this serves to prevent areduction of the operating speed.

According to the second embodiment, the number of the clock generationcircuits is reduced; therefore, this serves to decrease the chip area.

Third Embodiment

According to the second embodiment, one of the first, second chips 71,72 and the controller 73 outputs the clock signal. Based one the clocksignal, the first, second chips 71, 72 and the controller 73 areoperated.

On the contrary, according to the third embodiment, the controller 73controls program and verify read operation of the first and second chips71 and 72. Specifically, the controller controls the first and secondchips 71 and 72 so that the generation timing of the first and secondchips 71 and 72 is not overlapped. In this case, the first, second chips71, 72 and the controller 73 have no need of mutually monitoring theoperating state. Thus, the first and second chips 71 and 72 have no needto include the monitor circuit MNT. Therefore, according to the thirdembodiment, the circuit configuration is simplified as compared with thefirst and second embodiments.

According to the third embodiment, the controller 73 controls the firstand second chips 71 and 72. The present invention is not limited to thisconfiguration. For example, one of the first and second chips 71 and 72may control the other thereof and the controller 73. In this case, oneof the first and second chips recognizes whether or not address is ownor other address.

Fourth Embodiment

According to the foregoing first to third embodiments, a plurality ofchips comprising a NAND flash memory as a high-voltage generationcircuit for program and verify read operations. On the contrary,according to the fourth embodiment, all NAND flash memory chips do notinclude the high-voltage generation circuit, and the followingconfiguration is employed. Specifically, the controller 73 or one orsome chips only of the NAND flash memory chips has a high-voltagegeneration circuit.

FIG. 22 shows the configuration of an MCP or memory card according tothe fourth embodiment. For example, FIG. 22 shows the case where thecontroller 73 includes a high-voltage generation circuit 90. Thecontroller 73 supplies a control signal for controlling each operationof the first and second chips 71 and 72 based on the commands suppliedto the first and second chips 71 and 72. The high-voltage generationcircuit 90 of the controller 73 supplies a voltage required for programand verify read operations to one of the first and second chips 71 and72, which are in an operating state according to the control signal.

In other words, the controller 73 carries out the following control.Specifically, one of the first and second chips 71 and 7 attains acurrent peak mode of program, read or verify read operation based on thecommand. In this case, when the other of the first and second chips 71and 72 comes into the current peak mode of read or verify readoperation, the controller 73 sets it to a wait state using the controlsignal. In this state, the high-voltage generation circuit 90 supplies avoltage required for the operating state chip. Thereafter, when thesupply of high voltage required for program, read or verify readoperation ends, that is, when the peak current ends, the controller 73set the waiting state chip to an operating state, and then supplies avoltage required for the chip. For example, the read operation issmaller than the write operation in the current peak. Thus, in the caseof the read operation, the high-voltage generation circuit may su highvoltage to several chips.

According to the fourth embodiment, one high-voltage generation circuit90 included in the controller 73 supplies high voltage to the first andsecond chips 71 and 72. Thus, it is possible to prevent the peak currentfrom being overlapped, and to reduce large current consumption. Ingeneral, according to the following high voltages, load increases whenthe word line rises. One of the high voltages is a program voltage Vpgmused in the program operation, and another is a voltage Vpass forsetting a non-select cell to a conductive state. Another is a readvoltage used in read or verify read operation. For this reason, if thefirst and second chips 71 and 72 simultaneously attain an operatingstate, the high-voltage generation circuit 90 requires performancecapable of charging two times loads.

However, according to the control of the fourth embodiment, the firstand second chips 71 and 72 having a NAND flash memory do notsimultaneously attain an operating state. Therefore, the high-voltagegeneration circuit is sufficient in having performance capable ofcharging load equivalent to one chip. In addition, one high-voltagegeneration circuit only is used; therefore, the circuit configuration issimplified.

FIG. 23 shows the configuration of an MCP or memory card according to amodification example of the fourth embodiment. According to the fourthembodiment, the controller 73 supplies the control signal to the firstand second chips 71 and 72. The high-voltage generation circuit 90supplies a high voltage required for one of the first and second chips71 and 72. The supply of the high voltage is made based on the controlby the controller 73.

On the contrary, according to the modification example, the first andsecond chips 71 and 72 generate a request signal for requesting thesupply of high voltage. When the request signal is supplied, thecontroller 73 supplies a high voltage to one of the first and secondchips 71 and 72, which first generates the request signal. Thus, thechip supplied with the high voltage attains an operating state;conversely, the chip supplied with no high voltage attains a wait state.Thereafter, when the supply of the high voltage ends, the high voltageis supplied to the waiting state chip. The foregoing configuration isemployed, and thereby, it is possible to prevent the peak voltage frombeing overlapped, and to reduce large current consumption.

The fourth embodiment was described, referring to the case where ahigh-voltage generation circuit is provided for a controller or for someof a plurality of chips, and a high voltage is supplied to predeterminedones of the chips. However, the present invention is not limited tothis, and a high-voltage generation circuit whose boosting capability isrelatively low may be provided for each of the first and second chips 71and 72, as shown in FIGS. 26 and 27. FIG. 26 illustrates the case wherethe first chip 71 uses a high voltage. In this case, the high-voltagegeneration circuits of the first and second chips 71 and 72 are operatedsimultaneously, and the output voltages of these high-voltage generationcircuits are supplied to the word line drive circuit or another elementof the first chip 71. FIG. 27 illustrates the case where the second chip72 uses a high voltage. In this case, the high-voltage generationcircuits of the first and second chips 71 and 72 are operatedsimultaneously, and the output voltages of these high-voltage generationcircuits are supplied to the second chip 72. FIGS. 26 and 27 show anexample of a two-chip configuration, but three-chip configuration may beused instead. Furthermore, only the selected ones of the high-voltagegenerating circuits of the chips may be operated.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A semiconductor memory system comprising: a firstsemiconductor memory device; a second semiconductor memory device; afirst voltage generation circuit configured to generate voltage for thefirst semiconductor memory device; and a second voltage generationcircuit configured to generate voltage for the second memory device;wherein the first and second voltage generation circuits are drivensimultaneously and co-supply a necessary voltage to one of the first andsecond semiconductor memory devices when the necessary voltage is beyondcapability of each one of the first and second voltage generationcircuits.
 2. The system according to claim 1, wherein the first andsecond voltage generation circuits have capability to generate voltagerelatively lower than necessary peak voltage for each of the first andsecond semiconductor devices.
 3. The system according to claim 1,wherein the first voltage generation circuit is provided in the firstsemiconductor memory device and the second voltage generation circuit isprovided in the second semiconductor memory device.
 4. The systemaccording to claim 1, further comprising: a first word line drivecircuit provided in the first semiconductor memory device; and a secondword line drive circuit provided in the second semiconductor memorydevice, wherein the necessary voltage is supplied to one of the firstand second word line drive circuits from the first and second voltagegeneration circuits when the necessary voltage is beyond capability ofeach one of the first and second voltage generation circuits.
 5. Thesystem according to claim 1, further comprising a controllerelectrically connected to the first and second voltage generationcircuits, wherein a program operation and a verify operation in thefirst and second semiconductor memory devices are controlled by thecontroller.
 6. The system according to claim 1, wherein each of thefirst and second semiconductor memory devices is a NAND flash memory.